Method and an apparatus for analyzing a material

ABSTRACT

A method and an apparatus for analyzing a material, such as coal and iron ore, particularly with a view to identifying contaminants, is disclosed. The method and apparatus are based on the use of multiple (particularly dual) energy x-ray analysis with x-rays at different photon energies. X-rays are transmitted through a material and the detected x-rays are processed to produce an image of the material that combines together the separated images produced by the different photon energy x-rays. The combined image has enhanced contrast which minimizes the affects of non-compositional factors that otherwise would affect identifying constituents of the material.

The present invention relates to a method and an apparatus for analysinga material produced in the minerals industry to obtain information onthe composition, type, or form of the material.

UK patent application GB 2083618 in the name of Outokumpu Oy describes amethod and apparatus for analysing ore which is based on the use of twosources of gamma radiation each having different levels of energy. Inaccordance with the disclosure in the UK patent application,lumps/particles of ore are allowed to fall, one by one, past an assemblywhich comprises two pairs of sources of gamma radiation and an energydispersive detector. The gamma radiation sources and the detector arepositioned so that the detector receives back-scattered radiation. Thepassage on column 1 lines 99-113 describes that:

"Thus the essential feature of the invention is that a piece of rock orother ore sample is irradiated by means of two γ-ray sources each havinga different intensity of energy. The energy of one is selected so thatthe Compton effect is predominant. The energy of the other is selectedso that the photoelectric effect and the Compton effect compete witheach other. The photoelectric effect is strongly dependent on theordinal number of the element (i.e. its atomic number), whereas theCompton effect is independent of the ordinal number. By measuring theratio of the intensities of these two scatters having different levelsof energy, a quantity is obtained which represents the proportion ofheavy elements in the rock."

Accordingly, the UK patent application relies on dual energy gammaradiation to determine the proportion of heavy elements in alump/particle of ore and this information provides a basis todistinguish valuable ore from gangue.

An object of the present invention is to provide an improved method andapparatus for analysing a feed material produced in the mineralsindustry.

According to the present invention there is provided a method ofanalysing a material produced in the minerals industry which comprisesthe following steps:

i. directing x-rays at different photon energies onto the material;

ii. detecting x-rays transmitted through the material;

iii. processing data relating to the detected x-rays of step (ii)obtained at the different photon energies to minimise the effects ofnon-compositional factors on the data and thereby to obtain from theprocessed data information on the composition, type, or form of thematerial.

The term "material" is understood herein to mean any material producedin the minerals industry, including, but not limited to, ores, minerals,or fossil fuels.

The material may be in an as-mined or in a processed form. For example,depending on the particular mineral deposit, the material may be in theform of, but not limited to, particles, lumps, fines, rocks,conglomerates, agglomerates, or aggregates.

The term "analysing" is understood herein in the broadest context andincludes, but is not limited to, analysing a material for the purpose ofdetecting the presence of particular constituents of the material,identifying/measuring the constituents of the material, anddiscriminating between different constituents of the material.

The term "non-compositional factors" is understood herein to includefactors such as the density and/or the thickness of a material which,together with the composition of the material, affect theabsorption/transmission of x-rays that are incident on the material.

The present invention is based on the realisation that there is a widerange of applications in the minerals industry in which multiple(particularly dual) energy x-ray analysis can be used to minimise theeffects of non-compositional factors on data generated in x-ray analysisof a material, which factors would otherwise make it difficult to obtaininformation on the composition, type, or form of the material by meansof analysis of that data. The technique of dual energy x-ray analysis isbased on processing data of detected transmitted x-rays obtained atdifferent photon energies. Such processing makes it possible to minimisethe effects of non-compositional factors on the detected data so thatthe detected data provides clearer information on the composition, type,or form of the material.

The range of applications for multiple energy x-ray analysis in themineral industry include, but is not limited to, sorting material on thebasis of composition, type, or form. One, although by no means the only,application of interest to the applicant is sorting contaminantparticulate material and coal. Another application of interest to theapplicant is sorting iron ore rocks on the basis of the grade of iron inthe rocks.

In the context of sorting a material based on composition, type, orform, it is preferred that the method further comprises step (iv) ofidentifying a constituent of the material on the basis of composition,type, or form.

It is preferred that the method further comprises step (v) of separatingthe identified constituent from the material.

In particular, according to the present invention there is provided amethod of sorting a material produced in the minerals industry whichcomprises the steps of:

i. feeding a stream of the material through a gap between a source ofx-rays and a detector of x-rays;

ii. operating the x-ray source to direct x-rays at different photonenergies towards the x-ray detector;

iii. operating the detector to detect x-rays received from the x-raysource to generate data for each section of the stream of the materialthat passes through the gap;

iv. identifying a constituent of the material by processing the data tominimise the effects of non-compositional factors relating to thematerial that otherwise would affect the identification of theconstituent to thereby detect the constituent; and

v. separating the constituent from the material.

In one particular application of the present invention it is preferredthat the material comprises coal and a contaminant.

The term "contaminant" is understood herein to mean a material that isnot regarded as a valuable product that is mixed with a valuablematerial, such as coal.

It is noted that the constituent may be a valuable material and not acontaminant.

The x-ray source may comprise two or more separate x-ray tubes operatingat different voltages.

With such an arrangement, the x-ray detector may comprise two or moreseparate arrays of x-ray detectors.

Alternatively, the x-ray source may comprise a single x-ray tubeoperating at a selected voltage.

With such an arrangement, the x-ray detector may comprise two or moreseparate arrays of x-ray detectors. There may be one or more filteringmeans associated with each detector array.

For example, the separate arrays of the x-ray detectors may be alignedso that x-rays transmitted through the material are detected by a firstarray and thereafter by a second array. With such an arrangement, thefirst array acts as a filtering means for the second array.

It is preferred that the first array absorbs and detects low energyx-rays and that the second array absorbs and detects higher energyx-rays.

Alternatively, the x-ray source may comprise a single x-ray tubeoperating at a modulated voltage.

With such an arrangement, the x-ray detector may comprise a singledetector array.

It is preferred that the maximum operating voltage of the x-ray sourcebe less than 300 kV.

It is preferred particularly that the maximum operating voltage of thex-ray source be less than 200 kV.

The constituent separation step (iv) may comprise discharging thematerial from the end of a conveyor belt and selectively operating aconstituent removal system to separate the detected constituent from thematerial in response to identification of the constituent in the dataprocessing step (iv).

It is preferred that the contaminant removal system be based on the useof air or any other suitable fluid to displace the constituent from apath of movement.

According to the present invention there is also provided an apparatusfor analysing a material produced in the minerals industry whichcomprises:

i. an x-ray transmission analysis system for directing x-rays atdifferent photon energies onto the material and detecting x-raystransmitted through the material; and

ii. a means for processing the data generated by the x-ray transmissionsystem to minimise the effects of non-compositional factors on the datato obtain from the processed data information on the composition, type,or form of the material.

It is preferred that the processing means be adapted to produce x-rayimages of the material at each photon energy.

The term "image" is understood herein to mean an image constructed froma time sequence of collected detector array measurements. The image maybe stored electronically and/or presented visually.

It is preferred particularly that the processing means be adapted toproduce a combined image of each of the different photon energy imageswhich has enhanced contrast between constituents of the material.

In the context of sorting a material based on composition, type, orform, it is preferred that the apparatus comprises a means foridentifying a constituent of the material based on composition, type, orform.

The material may be any suitable material. By way of example, thematerial may be run-of-mine coal or iron ore.

It is also preferred that the apparatus comprises a means for separatingthe identified constituent from the material.

The means for separating the constituent may be any suitable means.

In particular, according to the present invention there is provided anapparatus for sorting a material produced in the minerals industry toseparate a contaminant from the remainder of the material whichcomprises:

i. an x-ray transmission system for transmitting x-rays through a streamof the material and generating two x-ray images at different photonenergies of each section of the stream of the material;

ii. a means for processing the images to produce a combined image whichhas enhanced contrast between the contaminant and the remainder of thematerial to enable detection of the contaminant; and

iii. a means for separating the contaminant from the remainder of thematerial.

In one particular, although by no means exclusive, application of thepresent invention it is preferred that the material comprises coal.

It is preferred that the x-ray transmission system comprises a source ofx-rays and a detector of x-rays transmitted through the material.

With such an arrangement, it is preferred that the apparatus furthercomprises a means for feeding the stream of the material through a gapbetween the x-ray source and the x-ray detector.

The feed means may comprise a conveyor belt assembly extending throughthe gap.

Alternatively, the feed means may comprise a conveyor belt assemblyarranged to discharge the stream of the material so that the trajectoryof the discharged material extends through the gap.

The x-ray source may comprise two or more separate x-ray tubes adaptedto be operated at different voltages.

With such an arrangement, the x-ray detector may comprise two or moreseparate arrays of x-ray detectors.

Alternatively, the x-ray source may comprise a single x-ray tube adaptedto be operated at a selected voltage.

With such an arrangement, the x-ray detector may comprise two or moreseparate arrays of x-ray detectors with the arrays having differentfiltering means.

For example, the separate arrays of the x-ray detectors may be alignedso that x-rays transmitted through the material are detected by a firstarray and thereafter by a second array. With such an arrangement, thefirst array acts as a filtering means for the second array.

It is preferred that the first array absorbs and detects low energyx-rays and that the second array absorbs and detects higher energyx-rays.

Alternatively, the x-ray source may comprise a single x-ray tube adaptedto be operated at a modulated voltage.

With such an arrangement, the x-ray detector may comprise a singledetector array.

It is preferred that the maximum operating voltage of the x-ray sourcebe less than 300 kV.

It is preferred particularly that the maximum operating voltage of thex-ray source be less than 200 kV.

The method and the apparatus of the present invention as described abovehas a number of advantages over the arrangement disclosed in UK patentapplication GB2083618. For example, the use of transmitted rather thanback-scattered radiation enables more representative analysis.Furthermore, the generation of an image enables the position of aselected constituent/contaminant to be accurately determined and thisprovides an effective basis to subsequently separate theconstituent/contaminant. In addition, the use of image processing makesit possible to determine the shape of a constituent/contaminant andtherefore separation can be achieved on this basis. Furthermore, thepresent invention can operate at significantly lower energy levels thanthe levels of 300-1500 kV reported in the UK patent specification.Furthermore, the present invention is not restricted to the use ofcomplex energy dispersive detection.

The present invention is based on experimental work carried out by theapplicant which indicates that dual energy x-ray image analysis ofrun-of-mine coal which contains contaminants can be an effective basisfor sorting the coal on the basis of composition, type, or form. Thepresent invention is also based on experimental work carried out by theapplicant on iron ore.

In particular, the applicant has found in experimental work that dualenergy x-ray image analysis has the advantage of being able todistinguish contaminants from coal and to be able to distinguish ironore rocks on the basis of the grade of iron.

The applicant has found in the experimental work, in relation to coalthat dual energy x-ray analysis has the additional advantages of beingable to:

i. distinguish contaminants from any shale that is present in the run ofmine coal; and

ii. detect fine contaminants.

In the experimental work in relation to coal the applicant selected twox-ray images of a 65 mm bed of a sample of a run-of-mine coal at 50 kVand 85 kV voltage settings. The images were obtained by directing x-raysonto the bed and detecting x-rays transmitted through the coal by meansof x-ray detectors positioned beneath the bed.

The images had a high degree of coal bed variation, some shale, andcontaminants.

The images were processed by two separate computer programs based ondifferent algorithms to produce, in each case, a combined image of thetwo original images that enhanced differences in composition of the coaland the contaminants and minimised differences in other variables suchas density and the bed thickness.

The original and the combined images were further processed to obtainprofiles along the same line in all of the images. The line was chosento pass through the coal bed, some shale, and the contaminants. Theprofiles along the lines are shown in FIG. 1.

With reference to the figure, the two upper profiles are the profilesobtained from the original images at 50 kV and 85 kV energy levels. Itcan be seen from these profiles that there are significant variations insignal level across the profiles and these significant variations makesit difficult to discriminate on the basis of composition. Thesesignificant variations are the result of the effect of compositionalfactors and non-compositional factors such as density and thickness onabsorption/transmission of x-rays.

The lower two profiles in the figure are the profiles obtained from thecombined images using methods 1 and 2, respectively. It can be seen thatthe effect of the methods is to reduce significantly the variations insignal level across the profiles by minimising the effect ofnon-compositional factors on the data with the result that thevariations in signal level are attributable to composition. It can beseen that both processing methods enhanced the image of the contaminantsabove that of the coal bed and the shale and, as a consequence, thecombined images produced by both processing methods provided a basis todistinguish contaminants from valuable coal and shale.

The applicant carried out experimental work to investigate thefeasibility of separating detected contaminants from run-of-mine coal.

The experimental work was carried under conditions that were designed tosimulate sorting conditions associated with contaminants removal fromcoal which is transported via a conveyor operating at a feed rate of 600tph at a belt speed of 3.7 to 4 m/s.

The experimental work was carried out on a test-rig which comprised ahopper having an adjustable outlet gate which supplied run-of-mine coalwhich contained contaminants onto a variable speed conveyor beltarranged to form a 220 mm wide stream. The conveyor belt discharged thestream in a trajectory that cleared a splitter plate so that acceptablecoal was chanelled into an "accept" bin on one side of the splitterplate.

The test rig also included a blast array that was positioned adjacent tothe trajectory to separate contaminants from the coal. The followingblast arrays were tested:

i. 3 blast valves connected via hydraulic hosing to nozzles in line, at50 mm centres between the nozzles, and with each nozzle being 12 mm IDround flattened into a fan profile;

ii. 3 blast valves connected via hydraulic hosing to nozzles in line, at50 mm centres between the nozzles, and with each nozzle being 12 mm IDround;

iii. 5 blast valves connected via hydraulic hosing to 12 mm ID roundnozzles at 25 mm spacing between centres of the nozzles; and

iv. 1 1.5 inch 3-way blast valve with a 32 mm ID round nozzle.

The blast arrays were connected via a manifold to an air reservoir of700 kPa for most of the experimental work and for 400 kPa for theremainder of the test work.

The test rig also included a detector system for detecting contaminantsin the stream of coal which was coupled to the blast arrays to activateselectively the blast arrays to displace detected contaminants from thetrajectory.

The experimental work on the test rig established that contaminantscould be removed effectively from an airborne stream of run-of-mine coalpresented at conveyor belt speeds of up to 4 m/s without significantloss of coal.

Many modifications may be made to the preferred embodiment of thepresent invention without departing from the spirit and scope of thepresent invention.

In this regard, whilst the above-described experimental work relates torun-of-mine coal, the present invention is not so limited and extendsgenerally to materials produced in the minerals industry.

Furthermore, whilst the above-described experimental work relates toprocessing feed material in which the valuable material is the bulk ofthe feed material, the present invention is not so limited in scope andextends to situations in which the bulk of the feed material is gangue.

What is claimed is:
 1. A method of sorting a material produced in theminerals industry which comprises the steps of:i. feeding a stream ofthe material through a gap between a single x-ray tube operating at aselected voltage and two or more separate arrays of x-ray detectors; ii.operating the x-ray tube and directing x-rays of different photonenergies towards the x-ray detectors; iii. operating the detectors anddetecting x-rays received from the x-ray tube and generating data ofdetected transmitted x-rays obtained at different photon energies foreach section of the stream of the material that passes through the gap;iv. identifying a constituent of the material by processing the data ofdetected transmitted x-rays obtained at different photon energies tominimise the effects of non-compositional factors relating to thematerial that otherwise would affect the identification of theconstituent to thereby detect the constituent; and v. separating theconstituent from the material.
 2. The method defined claim 1 wherein theconstituent is a contaminant and the separation step (iv) comprisesdischarging the material from the end of a conveyor belt and selectivelyoperating a contaminant removal system to separate the contaminant fromthe material.
 3. An apparatus for sorting a material produced in theminerals industry to separate a contaminant from the remainder of thematerial which comprises:i. an x-ray transmission analysis system fordirecting x-rays at different photon energies onto the material anddetecting x-rays transmitted through the material, the system comprisinga single x-ray tube adapted to operate at a selected voltage and two ormore separate arrays of x-ray detectors; and ii. a means for processingthe data generated by the x-ray transmission system to minimise theeffects of non-compositional factors on the data to obtain from theprocessed data information on the composition, type, or form of thematerial.
 4. The apparatus defined in claim 3 wherein the processingmeans comprises a means to produce x-ray images of the material at eachphoton energy.
 5. The apparatus defined in claim 4 wherein theprocessing means comprises a means to produce a combined image of eachof the different photon energy images which has enhanced contrastbetween constituents of the material.
 6. The apparatus defined in claim1 wherein the apparatus further comprises a means for feeding the streamof the material through a gap between the x-ray tube and the x-raydetectors.
 7. The apparatus defined in claim 6 wherein the feed meanscomprises a conveyor belt assembly extending through the gap.
 8. Theapparatus defined in claim 6 wherein the feed means comprises a conveyorbelt assembly arranged to discharge the stream of the material so thatthe trajectory of the discharged material extends through the gap.